Various forms of ink jet apparatuses have been developed for jetting liquid (or solid, hot melt) materials, such as inks, adhesives, modeling materials, and the like. One widely accepted ink jet apparatus configuration involves a plurality of individual ink jet devices arranged in one or more rows, each fed by a common ink manifold. Such an arrangement is employed in the ink jet apparatus described in U.S. Pat. No. 4,418,355 to DeYoung et al., issued Nov. 29, 1983 (incorporated herein by reference). The apparatus described by DeYoung et al. includes a row of ink jet devices which are individually controlled to eject droplets of ink in response to jetting impulses produced by transducers 204.
The DeYoung et al. ink jet apparatus is composed of a number of layered plates (best shown in FIG. 2 of the DeYoung et al. patent) which form numerous ink passages, reservoirs and chambers. For example, when constructed (with reference to FIG. 1 of the DeYoung et al. patent), the layered plates form a plurality of ink jet chambers 200 which are fed ink from a common reservoir manifold 212, through restrictor openings 214 in a restrictor plate member 216. The restrictor plate with the restrictor openings provides communication passages for delivering ink from the common reservoir manifold to each ink jet chamber. Embodiments of the present invention relate to improved restrictor members and ink jet apparatuses and processes employing the same.
For most solid ink or liquid ink jet apparatuses, air in the ink passages and chambers is one of the major contributing factors leading to jet outages in which the ink in an ink jet chamber of the apparatus is not jetted properly. Jet outages tend to occur when air bubbles trapped in the ink jet chamber of the apparatus absorb enough of the pressure applied by an energized transducer to inhibit the transfer of pressure to the ink or other liquid in the ink jet head.
The jet outages caused by trapped air bubbles seem to be more prevalent among hot melt or solid ink jet apparatuses, in which the ink exhibits a phase change during the "cold" start sequence. During the "cold" start sequence, a solid ink is liquified by being heated, so that the ink can be jetted for printing. The liquified ink again solidifies after a printing procedure is finished. Since the ink shrinks in volume during the solidification process, air pockets tend to form in the ink reservoir and flow paths within the apparatus. These air pockets create air bubbles in the ink during the next "cold" start sequence in which the ink is heated and liquified again. The air bubbles created during the "cold" start sequence can flow with the ink into the ink jet chambers and cause jet outages.
In order to remove unwanted air bubbles in the ink jet chambers, typical ink jet apparatuses have been equipped with air bubble purge systems which enable an operator to purge air bubbles trapped in the ink jet chambers. Pressurization and vacuum methods have been used to purge air bubbles.
Ink in a typical multi-jet ink jet apparatus flows from an ink reservoir to an ink manifold and then to a plurality of ink jet chambers through restrictor openings. A typical ink jet chamber has a restrictor on one end and an ink jet ejection orifice on the other end. The restrictor defines an opening through which ink passes from the manifold to the ink jet chamber. Conventional ink jet apparatuses employ a restrictor member, as shown in the De Young et al. patent, having openings that are each symmetrical with respect to a vertical center line. Such a conventional restrictor opening is shown herein in FIG. 3a. Referring to FIG. 3a, the opening 7 of the restrictor 9 has a circular upper portion 3, a rectangular lower portion 5 and a throat 4 connecting the upper portion 3 with the lower portion 5. An imaginary vertical center line 2 divides the opening 7 into two symmetrical (mirror image) halves. The throat 4 is located in the center of the opening 7, coaxial with the vertical center line 2.
The ink flow through the opening 7 of the restrictor 9 is represented by arrow 11 in FIG. 3a. FIG. 3b shows a cross-sectional view of the ink flow direction 11 through an ink jet chamber 14, the restrictor 9 and an ink manifold 240 of an ink jet apparatus. As shown by FIGS. 3a and 3b, the ink flow 11 can result in the conveyance or formation of air bubbles 50 in the ink jet chamber 220. Some air bubbles 50, especially the ones trapped in corners of the ink jet chamber, are not pushed toward the ink droplet ejection orifice 210 by the ink flow 11 and become trapped within the ink jet chamber. As a result, pressure pulse caused by actuations of the transducer 270 are at least partially absorbed by the air bubbles 50, instead of being fully transferred to the ink within the ink jet chamber for ejecting droplets.